Where the tank is mounted depends on where the engine is, and on space and styling. Safety demands that it is positioned well away from heated components, and outside the passenger compartment.
Most tanks are made of tinned sheet steel that has been pressed into shape.
Some passenger car tanks are made of non-metallic materials. Aluminium or steel is used on commercial vehicles.
The tank is usually in two parts, joined by a continuous weld around the flanges where the parts fit together. Baffles make the tank more rigid.
They also stop surging of fuel and ensure fuel is available at the pickup-tube.
Fuel expands and contracts as temperature rises and falls. So fuel tanks are vented to let them breathe.
Modern emission controls prevent tanks being vented directly to the atmosphere. They must use evaporative control systems.
Vapor from the fuel tank is trapped in a charcoal canister, and stored there, until it is burned in the engine. A vapor or vent line with a check valve connects the space above the liquid fuel with the canister. This valve opens when pressure starts to rise, and lets vapor through, but not liquid.
Liquid fuel closes the check valve and blocks the line, stopping liquid fuel reaching the charcoal.
Some systems have a small container, called a liquid-vapor separator, above the fuel tank. It also prevents liquid fuel reaching the charcoal.
This gasoline tank has a small separator tank and a number of vents.
They’re from different parts of the tank so that for as many vehicle positions as possible, at least one is always above the level of gasoline in the tank.